The present disclosure is related to a projection zoom lens and a projection type display device. The present disclosure is related to a projection zoom lens which is suited to magnify and project original images which are formed by light valves onto a screen, for example, and a projection type display device equipped with such a projection zoom lens.
Conventionally, projection type display devices that utilize light valves, such as liquid crystal display elements, DMD's (Digital Micromirror Devices: registered trademark), etc., are in wide use. Particularly, projection type display devices of configurations that employ three light valves, each corresponding to illuminating light beams of the three primary colors, red, green, and blue, combine light beams which are modulated by each of the light valves with a prism or the like, and display images on screens via a projection lens, are in wide use.
It is necessary for projection lenses, which are utilized in projection type display devices that combine light beams modulated by three light valves with a color combining optical system, to have a long back focus in order to provide the aforementioned prism or the like that combines colors, and also to avoid problems related to heat. Further, the spectral properties of color combining prisms change according to the incident angles of light beams that enter thereinto. Therefore, it is necessary for projection lenses to be configured such that the entrance pupils thereof are sufficiently distantly positioned when the reduction side is the light incident side. That is, it is necessary for the projection lenses to have telecentric properties at the reduction side.
Known projection zoom lenses that satisfy the above demands to a certain degree are disclosed in Japanese Patent Nos. 5397562 and 5081045. Japanese Patent No. 5397562 discloses a projection zoom lens having a five group configuration, among which three lens groups move while changing magnification. Japanese Patent No. 5081045 discloses a projection zoom lens having a five group configuration, in which a first lens group provided most toward the magnification side is constituted by two lenses.